Loudspeakers and headphones can utilize an electrostatic transducer for sound reproduction that includes a tensioned conductive low-mass diaphragm positioned between a pair of conductive stator plates. Small air gaps may be present between the diaphragm and the stator plates, and the diaphragm may have a stationary charge relative to the stator plates. If no signal is applied to the stator plates, the diaphragm may be static and stays centered between the stator plates. When equal magnitude opposite-phase audio signals are applied to the stator plates, a net force imbalance may be created over the diaphragm, which displaces the diaphragm. In turn, the air adjacent to the diaphragm may be displaced to create sound corresponding to the audio signals.
As a result, loudspeakers and headphones using electrostatic transducers may have very low harmonic distortion, full bandwidth frequency response, and high fidelity sound reproduction, as compared to loudspeakers and headphones with moving coil transducers. Electrostatic transducers may have these characteristics due to the push-pull, constant charge electrostatic drive and the relatively low mass of the diaphragm. In particular, the low harmonic distortion may be due to the push-pull electrostatic drive and the nearly constant bias charge on the diaphragm. However, to generate sufficient and acceptable sound output with an electrostatic transducer, high voltages may be required for biasing the diaphragm and for the audio signals. Listeners of loudspeakers and headphones with electrostatic transducers may need to be adequately protected from the possibility of electric shock and fire because of the high voltages utilized.
Headphones may be of an open-back type or closed-back type, regardless of the type of transducer within the headphones. Whether a particular listener uses an open-back headphone or a closed-back headphone may depend on the application and personal preferences of the listener. Open-back headphones may have housings with backs that are open to the environment, which may allow ambient sound into the headphones and also allow sound from the headphones to escape into the environment. The sound produced in open-back headphones is generally considered more natural with an increased depth of field, as compared to closed-back headphones. However, open-back headphones are not typically used in recording applications because sound from the headphones may be picked up by recording microphones. In contrast, closed-back headphones may have housings with backs that are closed to the environment, which may block ambient noise into the headphones and also reduce the amount of sound from the headphones that can escape into the environment. Closed-back headphones may typically be used for studio monitoring and recording applications.
Earphones are a type of headphone that can be inserted into the ear canal of a listener. Earphones may provide better noise isolation due to their placement in the ear canal and use of acoustically sealing sleeves, as compared to headphones that are placed over the ear or earbuds that are placed on the outer ear. Typical earphones with electrostatic transducers may be of the open-back type. However, some listeners, such as professional musicians and performers, may prefer closed-back earphones to prevent sound leakage in recording applications and to block ambient noise, particularly when using the earphones as an in-ear monitor.
Accordingly, there is an opportunity for an earphone that addresses these safety and sound reproduction concerns. More particularly, there is an opportunity for a closed-back earphone with an electrostatic transducer that adequately protects a listener from electric shock due to the high voltages used, has high fidelity sound reproduction, and blocks ambient noise.